LADAR (laser radar, also referred to as lidar) is a technology to determine the distance to and/or position of objects. Additionally, LADAR systems may measure the relative velocity of objects and/or vibrations of objects.
LADAR systems include a laser to deliver light to the target object and an optical receiver to collect the return light. To reduce background light detected at the receiver, LADAR systems use optical filters with a bandwidth narrow enough to reject most scattered sunlight and other sources of background light, and wide enough to transmit substantially all of the return light. For LADAR systems that track high velocity targets (like aircraft and missiles), the Doppler shift of the return photons may limit the minimum useful bandwidth of the receiver filter. Therefore, the optical filters used in current LADAR systems have pass bandwidths wide enough to accept return light from stationary or moving targets (i.e., return light that is significantly Doppler shifted relative to the transmitted laser light). Where the filter bandwidth is wider than the laser linewidth, excess background light may be received by the LADAR receiver, decreasing the signal to noise ratio of the system. Where the filter bandwidth is about equal to the laser linewidth, return light from high velocity targets may be rejected, making such targets ‘invisible’ to the LADAR system. Therefore, techniques to increase the signal to noise ratio of LADAR systems while permitting tracking of high velocity targets are desirable.